I have one friend who tested at five weeks and got a negative pregnancy test. All signs pointed to pregnancy… except the tests. Then, at eight weeks, sure enough, she got a positive pregnancy test! While she never figured out why those initial tests were negative, there are some common explanations for why this might happen.

Even if you think you know how to take a pregnancy test, be sure to follow all of the instructions in the box. I know it sounds so obvious, but specific steps for each brand can vary. Here are a few general tips:

Read the results within the recommended time frame. Timing is so important—if you don’t wait long enough, the second line may not show up; if you wait too long, the second line could dry up. Bring a stopwatch or a watch with a second hand into the bathroom.
Have a full bladder. If there’s not enough urine on the applicator, the test won’t work properly—some tests specify urinating on the test for a full 20 seconds or more!
Use first morning urine. Though most instructions will tell you this is not necessary, there’s some evidence that it may help you get an accurate result. First morning urine often contains a greater concentration of hCG, the hormone at-home pregnancy tests detect.
Check the expiration date. An expired or faulty pregnancy test might not work properly.

Can You Be Pregnant and Have a Negative Pregnancy Test?

If you’re crossing your fingers for a positive pregnancy test, but get a negative pregnancy test instead, you’re probably wondering how accurate the reading is and whether it could be wrong. Though pregnancy tests are 99% accurate when used correctly, it’s possible you’ll fall into that 1%. What’s more?

A false negative is more common than a false positive, so there’s a chance you could be pregnant—especially if you already missed your period. (source)

What Causes False Negative Pregnancy Tests?

If you’re testing correctly and still getting a negative pregnancy test, here are some possible reasons why:

You’re testing too early

You’re eager, I get it! You want to rip open the package, pee on the stick, and see that second line. But if you test too early, your body won’t yet be producing enough hCG, the hormone produced once an embryo implants, for the test to recognize it and you’ll get a false result.

A good rule of thumb:

Take a pregnancy test on the day of your missed period.
If it’s negative, try again 2-3 days later.
If it’s still negative, test once more a week after your missed period—this is when pregnancy tests are most accurate.

You’re misinterpreting the lines on the test

How many of us have held a pregnancy test up to the light, searching for any sign of a line? Sometimes the line is too faint to know for sure, and it’s easy to misinterpret the lines. Check out my pregnancy tests below and read this post on pregnancy tests for more help deciphering those faint lines. And if you’re really having trouble, buy a digital pregnancy test that says ‘pregnant’ or ‘not pregnant’ after you test.

Your body doesn’t make as much hCG

While it’s rare, some women don’t produce enough hCG to ever get a positive at-home pregnancy test. If hCG levels double every 48-72 hours in 85 percent of pregnancies, that means they follow a different pattern in 15 percent of pregnancies. You can read more about this phenomenon in this post about hCG levels. In these circumstances, a blood test that detects hCG might be better since it’s more sensitive at picking up increased levels.

Even though most women have higher levels of hCG when pregnant with twins, there’s something called the high dose hook effect that can cause the test to be negative. (source)

This happens when hCG levels are unusually high. Why? A normal hCG test works by surrounding the hCG molecules with antibodies. The hook effect happens when the hCG levels are so high—like in a pregnancy with multiples—that the hormone saturates the antibodies and they don’t form around the hCG. Thus, you’ll get a negative pregnancy test, despite being pregnant—with twins!

Your pregnancy isn’t viable

I know firsthand how devastating miscarriage can be. But sadly, 10 to 20 percent of pregnancies end in early miscarriage. If you are far enough along, but still get a negative pregnancy test, there’s a chance there’s a complication with the pregnancy. This happens during:

An ectopic pregnancy: With an ectopic pregnancy, the fertilized egg plants itself in the fallopian tube rather than the uterus. You’re technically pregnant, but because the egg implanted in the wrong location, it won’t register on an at-home pregnancy test. Unfortunately, it’s not possible to carry an ectopic pregnancy to term and could lead to serious internal bleeding if not treated. Call your healthcare provider right away if you suspect you have one.
Gestational trophoblastic disease (GTD) or molar pregnancy: Caused by a fertilization error, a (GTD) or molar pregnancy causes the rapid growth of abnormal tissue. It rarely involves a developing embryo, but your body does begin to produce hCG. This leads to a false positive on a pregnancy test.

If your healthcare provider confirms an early miscarriage as the cause of your negative pregnancy test, know that you are not alone. There are so many women out there who share your pain, and the majority of them go on to have healthy pregnancies in the future. Take the time you need to grieve before trying again.

If You Retest and Still Get a Negative Pregnancy Test…

In most cases, this means you are simply not pregnant. Lifestyle factors that can cause a missed period include:

After a negative pregnancy test, wait a few days or up to a week to test again. If you still get a negative pregnancy test and you haven’t gotten your period, see your healthcare provider. They can help you rule out any other conditions that can cause a late or missed period.